278 MIMICRY AND NATURAL SELECTION 



Families inhabiting the same region, a tendency which is 

 so pronounced in the case of the Ithomiinae and Helico- 

 ninae that they were long regarded as a single group, 

 although the structural differences between them, as larva, 

 pupa, and imago, are strongly marked and indicate that 

 the first Sub-Family belongs to one side of the great 

 Nymphalid family and the second to the opposite side. 

 This remarkable uniformity in the species of certain 

 butterfly Sub-Families was first explained by Professor 

 Meldola * on the lines suggested by Dr. Fritz Miiller 2 in 

 1879, viz. as an adaptation in order to reduce the amount 

 of life sacrificed during the period when young and inex- 

 perienced insect-eating animals are learning to distinguish 

 between palatable and unpalatable (and perhaps unwhole- 

 some) food. If two species living intermingled and 

 equally numerous are superficially exactly alike, and both 

 nauseous, each will lose only half the number of indivi- 

 duals which would have been required in order to educate 

 their enemies if they had been dissimilar. The sacrifice 

 of life is also reduced by the strong general resemblance 

 running through the species of each specially protected 

 Sub-Family in one country. Such resemblance is by no 

 means confined to the Rhopalocera (butterflies) or the 

 Lepidoptera. It is found abundantly in all specially 

 defended insect Orders, principally the Hymenoptera. 

 If we look at the Australian Aculeata we notice a large 

 group of species in which the orange ground colour is 

 deeper and browner than in banded Aculeata generally, 

 while the black zones are broader and fewer, being in fact 

 usually reduced to two, one crossing the thorax, another 

 the abdomen. This very characteristic appearance is to 

 be found in Abispa, Eumenes, A las for, Odyneriis.Bembex 

 and probably many other genera : it also occurs in mimetic 

 Diptera (Asilidae), and Longicorn Coleoptera. Here is 

 a broad fact which receives an intelligible explanation by 

 Natural Selection, but by no other theory which has been 

 suggested. We can well understand, on the theory of 

 Natural Selection, why the members of specially defended 



1 Ann. Mag. Nat. Hist., Dec. 1882, p. 417. 



* Kosmos, May 1879, p. 100; also Kosmos, v, 1881. 



